Radiation source



March 4, 1958 H. M. BARTON, JR

RADIATION SOURCE Filed Sept. 10, 1954 mm on INVENTOR H. M. BARTON, JR.mm W Q} A 7' TORNE VS RADIATION SOURCE Hugh M. Barton, Jr.,Bartlesville, kla., assignor to Phillips Petroleum Company, acorporation of Betaware Application September 10, 1954, Serial No.455,130

7 Claims. (Cl. 315-104) This invention relates to apparatus forsupplying electromagnetic radiation of constant intensity. in onespecific aspect it relates to a spectrographic source to supplyultraviolet radiation for optical analysis instruments.

A large number of optical instruments has recently been developed forthe analysis of sample streams in terms of the radiation absorptionproperties thereof. Included in these instruments are those analyzerswhich employ radiation in the ultraviolet spectrum. Such radiation iscommonly produced by electrical discharge tubes filled with a gas suchas hydrogen or xenon, for example. In most of these optical analyzers itis important that the radiation source be of constant intensity in orderthat fluctuations in the measured radiation be indicative solely ofchanges in radiation absorbed by the material being analyzed. Thisrequires that a constant current be passed through the discharge tube toprovide constant illumination. However, the constant current cannot beobtained from a conventional constant voltage source because the voltagerequired to fire the tube initially is of considerably greater magnitudethan the voltage needed to sustain the discharge following the initialfiring of the tube.

In accordance with the present invention there is provided an improvedsource of constant intensity electromagnetic radiation. This radiationis emitted from a gas filled electrical discharge tube which isenergized by the passage of a constant direct current therethrough. Thedirect current is in turn derived from a source of alternating current.The input of a voltage regulator is connected to an alternating voltagesource to provide an alternating voltage source of constant amplitude.The output of the voltage regulator is connected to the input winding ofa saturable reactor type of current limiting voltage regulatingtransformer. The output alternating voltage from this transformer isrectified, filtered and applied across the discharge tube. Thetransformer has the property of saturating on short circuit, and thuslimits the current supplied to the discharge tube. The voltage acrossthe output terminals of this second transformer prior to the firing ofthe discharge tube is considerably higher than the voltage across thedischarge tube when the tube is conducting.

Accordingly, it is an object of this invention to provide an improvedsource of constant intensity radiation for use with optical analysisinstruments.

Another object is to provide apparatus to supply a constant directcurrent to a gas filled electrical discharge tube.

Various other objects, advantages and features of this invention shouldbecome apparent from the following detailed description taken inconjunction with the accompanying drawing in which:

Figure 1 is a schematic circuit diagram of a first embodiment of theradiation source of this invention; and

atent Figure 2 is a schematic circuit diagram of a second embodiment ofthe radiation source.

Referring now to the drawing in detail and to Figure 1 in particular,there is shown a gas filled electrical discharge tube 10 of the heatedcathode type. This tube can be filled with hydrogen or xenon, forexample, so that radiation in the ultraviolet spectrum is emitted whenan electrical discharge takes place between the cathode 11 and the anode12 of tube 10.

The circuit of Figure l is energized from a voltage source 13 which cansupply power at 115 volts, 60 cycles, for example. The output terminalsof voltage source 13 are connected to the respective blades 14 and 15 ofa switch 16. Blades 14 and 15 engage respective terminals 17 and 18 ofswitch 16 to supply power to the circuit associated with discharge tube10. Switch terminals 17 and 18 are connected to the respective endterminals of the primary winding 20 of a constant voltage transformer21, which can be of the type described in U. S. Patent 2,143,745.Transformer 21 is constructed of a stack of I shaped laminations 22forming a core bar in abutting relation with the ends of legs 23 and 24-of a stack of E shaped laminations 25. Primary winding 2a is mounted onone end portion 26 of core bar 22. An output winding 27 is mounted onthe second end portion 28 of core bar 22. An auxiliary winding 29 ispositioned over winding 26 on portion 26 of bar 22. The center leg 30 ofthe E-shaped laminations 25 is spaced from bar 22 to form an air gap 31.One end terminal of auxiliary winding 29 is connected to the center tapof winding 27 and the second end terminal of auxiliary winding 29 isconnected to a first output lead 33 of the transformer. A capacitor 34is con nected between the end terminals of winding 27. One

end terminal of winding 27 is connected to the second output lead 35 ofthe transformer.

Leads 33 and 35 are connected to the respective end terminals of theprimary winding 37 of a second transformer 33 which also is of thesaturable reactor type. The physical structure of the core oftransformer 38 is generally similar to that of transformer 21 andcorresponding elements are designated by like primed reference numerals.The output winding 40 of transformer 38 is provided with a larger numberof turns than input winding 37 to supply a high voltage output to firedischarge tube lti. Transformer 38 differs from transformer 21 in thatthe auxiliary winding 29 of transformer 21 is omitted.

The center tap of transformer winding 44 is connected to the center tapof the secondary winding 42 of a conventional transformer 43. The endterminals of the primary winding 44 of transformer 43 are connected torespective output leads 33 and 35 of voltage regulating transformer 21.One end terminal of the transformer winding 4-2 is connected to thecathode 11 of tube 1 and to one terminal of the filament 45 of tube 10.The

second terminal of filament 45 is connected to the second end terminalof transformer winding 42 through a variable resistor 46. is applied tofilament .5 to heat cathode 11.

()ne end terminal of winding 40 of transformer 38 isconnected through aresistor to the anode of a mercury vapor diode 51. An indicating lamp552 is connected in shunt with resistor 50. The second end terminal oftransformer winding 40 is connected through a resistor 53 to the anodeof a second mercury vapor diode 54. An indicating lamp 55 is connectedin shunt with resistor 53. Lamps 52 and 55 indicate that diodes 51 and54 are operating. The filaments of diodes 51 and 54 are connected acrossthe end terminals of the secondary winding 57 of a conventionaltransformer 58.

In this manner a constant voltage'' The end "terminals ofthe primarywinding 59 of transformer '58 are connected to respective leads '33 and35'. The center tap of transformer winding 57 is connected through apairof series. connectedinductorsfil and .62 and a'milliammeter 63, t'o aterminal ,64 of .a' thermal time delay relay--65. first capacitor '66"is connected between the center ltap of 't'ransfoi'mer'winding '57 andlea'd 41, and a second capacitor '67 is .connectedibetween lead 41 andthejunction'betweeriinductors "61 "and 62.

Terminal '64 of rlayfis is connected to a movable bimetallic arm 68which'fen'gagesa stationary contact 69 when heated to a predeterminedtemperature by aheating element 70. The end'terminaljs of heatingelement 701are connected to respectivepower terminals :17 andls'ofiswitch' 1'6. Terminal 69*6Lrelay 65 is connected totheanodellof'discharge'tubeJIO.

Closure of'switchlld-jresults in voltagesource 13 being applied ito theprimarrwindi'ng of voltage megulating transformeriZ-l; Theoutput-voltage .of*this* transformer appearing between.'leads 33 'an'd35is maintained ata constant'v-alue irrespectiveitof minorfluctuations' inthe output of'voltagesource 13. The operation of transformer 21toprovidethis constant voltageoutput isdescribed in said Patent2,143,745.

"Theontput voltage of" transformer 21' is applied to the primarywindin'g37 of transformer '38. The output voltage of transformerSS- is rectifiedby diodes'51 and 54, filtered by the unit includinginductors 61 and 62and capacitors-66 and 67; andappliedacross-discharge tube 10.The'voltage'required tdfiretube 1'0 initially may be of the-order ofseveral hundred vol-tswhereas avoltage of less *than :one" hundredvolts' is "su'fi'i'cie'nt" to maintain the discharge. The "ratio of'turns between transformer windings' 37'and-40 is*adjustd'such that anoutput 'voltage oftherequired magnitude isprovided across tube "-tocause initial firing' thereof. The purpose of time delay relay 65-isltoprevent the application of voltage across tube .10 until cathode 11 is'heated by filament 45 to its operating temperature. This prevents arcingbetween the cathode and anode of tube 10.

LOnce: relay 65 is :closed, the rectifiedvoltage from transformerwinding 40. is applied across tube 10 to cause a'tdischarge toitake'place between thecathode and anode. .:This discharge: results in' the'fiow' of considerablecurrent through' tube:10, which is followed atonce bytthe. generation ofsaself inductance in winding 40 oftransformeri38. I'In' the absenceofxcurrent flow through transformerwinding 40, there is substantially no-flow of magnetic.flux'zthroughi-airgap.:31' because of thewhigh reluctance through lthis.path. -'-However, the effect of.

thergenerated; selfiinductancerin; winding 40 is to choke the magneticflux tending to pass through winding 40 from primar'yr-windingi 37. A:portion ofthis magnetic fillXLjSaihBl'GbY shuntedxthrough airgap 31' sothat'the current IflOWLIhIOUgh transformernwindingxiil is limited andregulated. ..Under these:conditions, ordinary :minor fluctuations inthexcharacteristic. of discharge tube 10 are small in comparisonwith-the reserve powerv capacity of transformer 38v sothat thecurrentflow through tube 10 remains: constantas long: as the voltage applied tothe primary winding 37- of transformer.38'remains-constant.Theiradiationfrom. tube-10 isthus maintained at constant intensity.

'In Figure 2 .thereris illustrated aisecond embodiment of: theradiation'source'. of. this .invention. Tube, 10 is replaced :by. a gas..filled discharge tube-75 of the cold cathode: type. The voltage supplysection of Figure 2 isaidenticalatosthat'of Figure-1 andtcorrespondingelements. .aresdesignated. by likenprimed reference numerals.Transformer. 21C.and-.38....are? shown schematically. The voltage.appeafingbetween thesrend terminals 1 of transformer windingAOZ :isapplied across; first; opposite terminalsl'76 and. 71.01. arfnll waverectifier bridgenetwork 78'. 'Ihe'first. output terminal .79.,bf-bridge.network .78 is. applied 10.." thecathodelfill of=tube 75. ..;"l he..,second 40 respectively.

75 to. a. loa .deviceagqi i gsa ehis n.

output terminal 82 of bridge network 78 is connected to the anode -83 of"tube "75 through series connected in "10 rifled-filtere andapp ie aerosfsasfi eslflissh rs abs 75 which pr des :the :desire non tan inteu ty.radiation.

F om the ore oin d s iptienitsh n h appatem that therei's providedinaccordance with thisinvention an improved sourceofgradiation'pf;constant intensity.

This radiation is provided bypassing a constant direct current throughan electrical discharge device. The currentjs supplied from a saturablereactor type of voltage regulating transformer' whichhas the property of'20 applyingahi-ghfiring voltage across the tubeinit'ially andmaintaininga steady cufrent thereafter to sustain the discharge. Theoutput voltage from this transformer-is rectified and filtered tomaintain a steady direct current. 'This' constant direct current-results in radiation of constant intensity.

-While" thisinvention-has "been" described in canine-- tion' withpresent preferred embodiments thereof, it

should be evident that the invention isnot limited thereto.

' What is claimed is:

rable reactor current'limiting transformer havingthe inputterminalsthereof connected tothe output terminals of said-sourceofalternating'voltage, and current-redi fying means "havingthe-inputterminals thereofconnected totheoutput terminals of saidtransformer, the output terminals: ofsaid' current rectifying meansbeing-con nected to the cathode and anode of said discharge-tube,

--2. Aesource. of electromagnetic radiation-comprising; in combination,a gas filled discharge tube having a cathodeland an anode, tea source.of alternating voltage, a voltage regulator-having the input.terminals'thereof connected across said voltage source,.asaturablereactor current limiting transformerhaving'the input terminalsthereof connected to the output terminalsof said voltageregulator,current rectifying.- means havingtheinput-terminals:thereofflconnectedto the-output terminals of-saidtransformer, and, current filter means havingi-theinput terminals;thereof connected; to; they outputterminalsmf said rectifying, means,-;the output terminals of said cu rrent-filter means;beingconnectedgto thecathoderand-an ode. of saiddischargetub especti ly- 3- Th combinatieninacor ance with laim zmhp in said saturable reactorcurrentli itingtransformer comprises a loop ofmagneticmaterial, a; primary -.-wind ingmounted onsaid lo op, a secondary winding mounted on .said loopin spacedrelationwith said primary Windi lg, and amass ofgmagneticrmaterialextendingfsubstantially acrosssaid loop between said primaryand secondary windings.

4. Apparatus for supplying direct current tqa-had device, requiring ahigh starting; voltage and hav are- 05 sistance which Varies inverselywith curren t fiowing" therethrough comprising-in combination, a-'source of-al-' ternating. voltage,- a --s'a'turablereacton-current-liniiting transformer having the inputterminalsthereofconnected to the output terminals of said source of alternatingvoltage,'. andzcurrent rectifyingemeans having the input .ter-

rninalsnthereof; connectedto-the outputterminals ,ofi, transfgrmen t otputiterm na sc a ai ;cnrw trecte fying means supplying said direct,current.

5 App t s pp y n 1 9.0 tent sl ts squin art na l ase-aa having aresistance which varies inversely with current flowing therethroughcomprising, in combination, a source of alternating voltage, a voltageregulator having the input terminals thereof connected across saidvoltage source, a saturable reactor current limiting transformer havingthe input terminal thereof connected to the output terminals of saidvoltage regulator, current rectifying means having the input terminalsthereof connected to the output terminals of said transformer, andcurrent filter means having the input terminals thereof connected to theoutput terminals of said rectifying means, the output terminals of saidcurrent filter means supplying said direct current.

6. A source of electromagnetic radiation comprising, in combination, agas filled discharge tube having a cathode, an anode and a cathodeheater filament, a source of alternating voltage, a voltage regulator,means including a switch connecting said source of alternating voltageto the input terminals of said voltage regulator, a saturable reactorcurrent limiting transformer having the input terminals thereofconnected to the output terminals of said voltage regulator, circuitmeans connecting the output terminals of said voltage regulator to theend terminals of said cathode heater filament, current rectifying meanshaving the input terminals thereof connected to the output terminals ofsaid transformer, current filter means having the input terminalsthereof connected to the output terminals of said rectifying means,means including a time delay relay connecting the output terminals ofsaid filter means to the anode and cathode of said discharge tube,respectively, and means energizing said relay at a predetermined timeinterval following closure of said switch.

7. The combination in accordance with claim 5 wherein said satura-blereactor current limiting transformer comprises a loop of magneticmaterial, a primary winding mounted on said loop, a secondary windingmounted on said loop in spaced relation with said primary winding, and amass of magnetic material extending substantially across said loopbetween said primary and secondary windings.

References Cited in the tile of this patent UNITED STATES PATENTS2,085,060 Young June 29, 1937 2,176,447 Vilkormerson Oct. 17, 19392,280,630 Cisin Apr. 21, 1942 2,757,318 Noel et a1. July 31, 1956

